When you already have an image placed on a page, you can change the image fitting options.

Right-click a real image on page (not a placeholder, not a dummy image), point to Fitting, and then select the fitting option.

Note: this is available since 2.1.

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Fit Image

Select Fit to fit one side of the image in the placeholder and to crop the other side. The placeholder will not change its dimensions.

Crop Image

Select Crop if the image is wider AND higher than the placeholder, or smaller. The placeholder will not change its dimensions. If the picture is smaller of the placeholder, it will be scaled to fit.

Resize

Select Resize to fit one side of the image to the placeholder and to scale the image to fit the other side. The placeholder will not change its dimensions. Warning: this may lead to the distortion of the image.